Silver alloy



Patented June 6,1939

UNITED ATES PATENT OFFICE-9 SILVER ALLOY Frans B. Hansel, Kenneth L. andJames W. Wiggl, Indianapolis, Ind., assign'orl to 1'. IL

characteristics.

Mallory a 00., Inc., Indianapolis poration of Delaware No Drawing.Application March 1s, 19:

Serial No,

This invention relates to a new silver alloy and is concerned moreparticularly with an alloy which has improved physical and electrical Itis one of the objects of the invention to provide a silver base materialwhich can be used for an electrical make and break contact, containingvery low contact resistance, having negligible material transfer, havinggreat resistance under. "severe electrical loads, to welding andsticking.

Another object of the invention is, to provide a new silver base alloy,which has greatly increased tensile strength, and which shows a greatimprovement in resistance to tarnishing and corrosion.

Other objects of the invention will be apparent from the followingdescription, taken in connection with the appended claims.

While a preferred embodiment of the invention is described herein, itis' contemplated that a considerable variation may be made in the methadof procedure and the combination of elements, without departing from thespirit of the inven- 'tion.

' The present invention comprises basically silver, to which has beenadded magnesium and cadmium. In the formation of the new alloy, it ispreferable to provide a composition of the materials specified in thefollowing proportions:

. Percent Magnesium .05 to 15 ('adminm ,5 to Silver Substantially thebalance The preferred range of magnesium is .1 to 8%, because up'to thatpercentage, the magnesium is taken up in alpha solid solution in silver,and we have found that silver and magnesium up to 8%, can be alloyedvery. readily and the cast ingots can be rolled, swaged, or .drawn intodesirable shapes, such as sheet; bar stock, wire, strip and.

the like.

Silver and cadmium form a solid solution up to 45%; therefore, alloys ofthe class described in the present patent, are ternary solid solutionsof magnesium, cadmium and silver.

Wehave investigated a series of compositions and have found that thefollowing alloys, which are given by way of example only, have shownvery excellent results, such as increased strength and increased tarnishresistance. The alloys have also shown particularly good electricalproperties if used in the form of electrical contacts.

Silver The ingredients in the. proportions named above, may be meltedtogether by conventional methods, and poured into suitable molds. m

It was found desirable to add the magnesium in the form of asilver-magnesium master alloy of high magnesium concentration. Alloys ofthis type have a lower melting point, and therefore will go readily intothe silver melt, Since silvermagnesium has a tendency to oxidize andform a dross, it has been found desirable to melt such alloys, either ina reducing or neutral atmosphere,

or use suitable fluxes, which cover the melt.

The addition of magnesium in the form of a master alloy has also reducedthe loss of magnesium, and therefore has, made it possible to hold.closer tolerances in chemical composition.

The resultant alloys within therange of ternary solid solutions haveelectrical conductivlties, ranging from 20 to International annealedcopper standard according to the respective compositions.

An alloy, for instance, containing 356% magnesium and 7% cadmium, had anelectrical con- 40 ductivity of 22%. The hardness of this material inthe as cast condition, was 26 Rockwell 1". After swaging 30%, thishardness increased to 85 Rockwell F. We'have found that a Brinellhardness of 70 to 130, can be easily obtained with 46 these types ofalloys with the proper amount of cold working.

The alloys of the class described have shown very excellent qualities,when used for electrical purposes. A comparison test was conducted 50were tested on a resistive inductive circuit, at 470 cycles per minute,and wherein the current flowing in the circuit was increasedperiodically, to obtain definite current values of alloys in the naturedescribed above, in comparison with contact materials produced in theprior art. The amount of material transfer of one contact to the other,was used as the prime method of comparison.

A most surprising result was found in this test. It was discovered thatcontacts of the type described, and more particularly ones formed froman alloy containing 3.5% magnesium and 7% cadmium, showed no materialtransfer whatsoever. Fine silver under the same conditions would show amaterial transfer of .010", and coin silver would show a materialtransfer of .011".

The test data is tabulated as follows:

i A Critical Transfer current height Amperec Fine silver 12 .010negative. Coin silver 11 .011" negative. $59k g*'-7.0% Cd3.5% Mg 12None.

The final contact resistance on these new alloys, the compositions ofwhich are given above, did not substantially exceed values obtained forfine silver, under identical test conditions. In fact, under thesesevere operating conditions, the contact resistance actually measured.28 milliohm for the alloy containing 3 magnesium,-

and 7% cadmium.

The alloys of the present invention have been found useful for a largenumber of electrical contact applications, such as for instance,sensitive direct current relays, over-load cut outs, voltage whereincontacts of similar physical dimensions regulators, indicating andrecording gaugers, thermostatic. controls, and the like.

The other uses on the new alloy are in the form of silverware, such asis being used for jewelry purposes, tableware, industrial and simi-'intended to cover the invention broadly, within the spirit and scope ofthe appended claims.

What is claimed is:

1. A silver base alloy consisting of magnesium .1 to 15%, cadmium .5 to25% and silver substantially the entire balance.

2. A silver base alloy consisting of magnesium .1 to 8%, cadmium .5 to25% and silver substantially the entire balance.

3. A silver base alloy consisting of magnesium 1 to 4%, cadmium .5 to25% and silver substantially the entire balance.

4. A silver base alloy consisting of magnesium 1 to 4%, cadmium 5 to 20%and silver substantially the entire balance.

5. A silver base alloy consisting of about 3.5% magnesium, about 7%cadmium and about 89.5% silver.

FRANZ R. HENSEL. IQIN'NETH L. EMMERT. JAMES W. WIGGS.

